1. Field of the Invention
This invention relates generally to chimney screens and more particularly to retrofit chimney top spark arresters.
2. Description of the Prior Art
There are a great number of chimney top spark arresters to be found in the prior art. Most of the prior art spark arresters have screened sidewalls, a perforate top, and an open bottom. The arresters often times include internal baffles designed to slow the ascent of embers and the like and are provided with means for attaching the open bottom of the structure over the top of a chimney.
A few examples of prior art spark arresters should suffice as an illustration of the pertinent prior art as a whole. In U.S. Pat. No. 2,133,506 H. Giese describes a box shaped spark arrester having four screen sidewalls and a screen top. A solid baffle plate 16 is suspended within the spark arrester to slow the ascent of the rising embers. A similar mechanism can be found in the spark arresting device of J. Slocum (described in U.S. Pat. No. 1,641,102) with the exception that the internal baffles are not solid but rather are constructed from a screen material. U.S. Pat. No. 2,058,694 of J. Johnson, and U.S. Pat. Nos. 1,709,884 and 1,997,204 of J. Slocum disclose spark arresters of similar construction to the spark arrester of U.S. Pat. No. 1,641,102.
The basic theory behind the operation of prior art spark arresters is that if the ascent of embers and sparks is sufficiently slowed down by the baffle plates the combusting materials will burn out or fall back into the chimney before being released into the ambient environment. The screen sidewalls and screen top of the spark arresters form a last line of defense to prevent the egress of potentially hazardous, burning particulate matter.
There are several problems with baffle designs of the prior art spark arresters. For one, the draught of the chimney is impaired resulting in less efficient fireplace operation. Also, if sparks and embers are not moved quickly through a chimney it is possible that they may ignite any combustible material that may have built up along the inner walls of the chimney. Furthermore, the sparks and embers may actually burn slower than if the spark arrester was not there because of the reduced draught of the chimney. In other words, the prior art spark arresters do not increase the burn rate of the sparks and embers but merely decrease their rate of egress into the ambient environment.